1. Field of the Invention
The present invention relates to a method for forming bottle trenches. In particular, the invention involves the formation of bottle trenches by liquid phase oxide deposition.
2. Description of the Prior Art
Generally speaking, capacitors widely used in dynamic random access memory (DRAM) are formed by two conductive layers (electrode plate) having an insulation layer between. The ability of a capacitor to store electric charges depends on the thickness of the insulation layer, surface area of the electrode plate and the electrical characteristics of the insulating material. In recent developments to reduce size of semiconductor elements to enhance integration density, memory cell area must be continuously reduced to hold a large number of memory cells, thereby increasing density. Meanwhile, the electrode plates of a capacitor in a memory cell must present sufficient surface area to store enough electric charge.
Nevertheless, since element size is continuously reducing, trench storage node capacitance of DRAM is decreasing as well. As a result, storage capacitance must be increased to maintain good operating performance for memory.
Currently, the method for increasing storage capacitance for DRAMs increases the width of the bottom of the trench, thereby increasing surface area to form a bottle-shaped capacitor. An example of the method for forming bottle trenches in Dynamic Random Access Memory (DRAM) devices is as follows. After the formation of a deep trench, sidewalls of the trench is then oxidized to form collar oxide. Nitride and poly are then deposited to cover the sidewalls and bottom of the trench. The poly layer is then oxidized, followed by forming photoresist at the bottom part of the trench. Oxide not cover by the photoresist is then removed. Next, the photoresist layer is stripped, followed by nitridation to form a nitride layer. Bottom oxide, bottom poly, top nitride and top poly are then sequentially etched. After the removal of collar oxide, a protective layer covering the top part of the trench is then formed. Bottle trench is then formed by enlarging the bottom part of the trench.
As the size of semiconductor device continues to decrease, the formation of a total number of five layers (oxide, nitride, TEOS, poly, oxide) in the trench requires much wet strip process at the bottom of the trench for follow-up striping of films. This easily creates many combined process window issues and makes the process even more difficult to control during mass production.
In order to overcome the above problems, an object of the invention is to provide an anti-collar method for forming bottle trenches by liquid phase oxide deposition, which can be adopted in 0.09 xcexcm or even finer generation of DRAMs without the necessity for formation of multiple layers in the trench.
In order to achieve the above objects, there is provided a method for forming bottle trench, comprising providing a substrate having a pad layer formed thereon, such that a trench is formed in a predetermined position, forming a masking layer at the bottom part of the trench, using liquid phase oxide deposition to form an LPD oxide layer on the sidewalls of the trench, removing the masking layer to expose the bottom part of the trench, subjecting the LPD oxide layer to annealing, and etching the bottom part of the trench not covered by the LPD oxide layer to form a bottle trench.
According to another embodiment of the invention, the method for forming bottle trenches, comprises providing a substrate having a pad layer formed thereon, such that a trench is formed in a predetermined position, forming a protective layer on the pad layer and on the sidewalls of the trench, forming a masking layer at the bottom part of the trench, using liquid phase oxide deposition to form an LPD oxide layer on the protective layer, removing the masking layer to expose the protective layer at the bottom part of the trench, subjecting the LDP oxide layer to annealing, removing the protective layer not covered by the LPD oxide layer, and etching the bottom part of the trench not covered by the LPD oxide layer to form a bottle trench.
According to the method for forming bottle trenches by liquid phase oxide deposition of the invention, the process for forming bottle trenches is made much simpler and allows for easier process control. Consequently, the LPD oxide also helps in terms of promoting overall quality and yield of DRAM processes.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the present invention.